The oxidation of phospholipids by free radicals and molecular oxygen is under investigation. Preliminary experiments have focused on the preparation and purification of lecithins. High pressure liquid chromatography has been found to be a useful method for the analysis of lecithin molecular species and the purity of synthetic or natural lecithins can be investigated by means of this technique. Studies on the oxidation of l-palmitoyl-2-linoleoyl lecithin has led to the isolation and characterization of lecithin hydroperoxides, the first-formed oxidation products of lecithin. Work is continuing along these lines. In particular, reverse-phase chromatography is being thoroughly investigated in lecithin isolation and purification. Further, oxidation of several lecithins is being investigated under a variety of different conditions. The goal is to provide information about membrane-phase oxidation.